yihleego opened a new issue, #4654:
URL: https://github.com/apache/rocketmq/issues/4654
When starting a broker instance with the default configuration, the
`ScheduleMessageService` will create 180 `DeliverDelayedMessageTimerTask`
objects per second, and 1800 `HandlePutResultTask` objects per second if
`enableAsyncDeliver` is `true`, which is **NOT** good for GC.
Let's see some code:
```java
public class MessageStoreConfig {
// By default, there are 18 levels.
private String messageDelayLevel = "1s 5s 10s 30s 1m 2m 3m 4m 5m 6m 7m
8m 9m 10m 20m 30m 1h 2h";
}
```
[ScheduleMessageService#start](https://github.com/apache/rocketmq/blob/00da3e7249d2339717d96f7ea2ab8e4a2fd4242c/broker/src/main/java/org/apache/rocketmq/broker/schedule/ScheduleMessageService.java#L141)
```java
private static final long FIRST_DELAY_TIME = 1000L;
private static final long DELAY_FOR_A_WHILE = 100L;
private static final long DELAY_FOR_A_PERIOD = 10000L;
private static final long WAIT_FOR_SHUTDOWN = 5000L;
private static final long DELAY_FOR_A_SLEEP = 10L;
public void start() {
if (started.compareAndSet(false, true)) {
// ignore
for (Map.Entry<Integer, Long> entry :
this.delayLevelTable.entrySet()) {
Integer level = entry.getKey();
Long timeDelay = entry.getValue();
Long offset = this.offsetTable.get(level);
if (null == offset) {
offset = 0L;
}
if (timeDelay != null) {
if (this.enableAsyncDeliver) {
// Create a HandlePutResultTask object for each level
if enableAsyncDeliver is true.
this.handleExecutorService.schedule(new
HandlePutResultTask(level), FIRST_DELAY_TIME, TimeUnit.MILLISECONDS);
}
// Create a DeliverDelayedMessageTimerTask object for each
level.
this.deliverExecutorService.schedule(new
DeliverDelayedMessageTimerTask(level, offset), FIRST_DELAY_TIME,
TimeUnit.MILLISECONDS);
}
}
// ignore
}
}
```
[ScheduleMessageService#DeliverDelayedMessageTimerTask](https://github.com/apache/rocketmq/blob/00da3e7249d2339717d96f7ea2ab8e4a2fd4242c/broker/src/main/java/org/apache/rocketmq/broker/schedule/ScheduleMessageService.java#L383)
```java
class DeliverDelayedMessageTimerTask implements Runnable {
@Override
public void run() {
try {
if (isStarted()) {
this.executeOnTimeup();
}
} catch (Exception e) {
// XXX: warn and notify me
log.error("ScheduleMessageService, executeOnTimeup exception",
e);
this.scheduleNextTimerTask(this.offset, DELAY_FOR_A_PERIOD);
}
}
public void executeOnTimeup() {
// ignore
// At the end of execution, a new DeliverDelayedMessageTimerTask
object will be created, and it will run after 100ms.
this.scheduleNextTimerTask(nextOffset, DELAY_FOR_A_WHILE);
}
public void scheduleNextTimerTask(long offset, long delay) {
ScheduleMessageService.this.deliverExecutorService.schedule(new
DeliverDelayedMessageTimerTask(
this.delayLevel, offset), delay, TimeUnit.MILLISECONDS);
}
}
```
[ScheduleMessageService#HandlePutResultTask](https://github.com/apache/rocketmq/blob/00da3e7249d2339717d96f7ea2ab8e4a2fd4242c/broker/src/main/java/org/apache/rocketmq/broker/schedule/ScheduleMessageService.java#L569)
```java
public class HandlePutResultTask implements Runnable {
@Override
public void run() {
// ignore
// At the end of execution, a new HandlePutResultTask object will be
created, and it will run after 10ms.
if (isStarted()) {
ScheduleMessageService.this.handleExecutorService
.schedule(new HandlePutResultTask(this.delayLevel),
DELAY_FOR_A_SLEEP, TimeUnit.MILLISECONDS);
}
}
}
```
---
So, it's better to use `ScheduledExecutorService#scheduleWithFixedDelay`
instead of creating unnecessary objects.
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